This invention relates to programmable thermostats having various setpoints occurring at various programmed times. In particular, this invention relates to the recovery of the temperature in the space governed by the thermostat when a change in programmed setpoint temperature is scheduled to occur at a particular time.
Programmable thermostats having a series of user selected setpoints occurring at different times of the day or week are well known. These user selected setpoints may vary widely depending on the time of day or week. For instance, the setback temperature for an unoccupied home or office space at different times of the day or week may be quite different than the setpoint temperature for the space when it is to be occupied. This may result in a large demand being placed on a heating or cooling system associated with the thermostat when recovering from the setback temperature.
Programmable thermostats have heretofore included a recovery feature that permits the activation of a heating or cooling system prior to the scheduled change in setpoint temperature. These programmable thermostats typically authorize the setpoint to incrementally change from a starting time that is often determined by the thermostat. These thermostats have moreover attempted to define the slope by which the setpoint temperature changes so as to eliminate or lessen the overshoot of the target setpoint temperature. These starting times and slopes are derived internally by the thermostat based on recent histories of recovery from setpoint by the thermostat. These starting times and slopes of changing temperature versus time will vary from day to day depending on the most recent histories of setpoint recovery. As a result, there is no predictable time or rate of setpoint recovery.